Apparatus and method for conductivity measurement including probe contamination compensation

• US 6,529,841 B2
• Filed: 04/24/2001
• Issued: 03/04/2003
• Est. Priority Date: 05/13/1998
• Status: Expired due to Term

• Current Assignee: Diversey Incorporated (Sealed Air)
• Original Assignee: JohnsonDiversey, Inc
• Inventors: Livingston, James W., Chan, Wai Yin Cedric, Cocking, Andrew J.
• Primary Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US09/841,783
• Publication Number:
  US 20010029435A1
• Time in Patent Office: 679 Days
• Field of Search: 702/30, 702/32, 702/50, 702/65, 702/64, 733/350.5, 324/439, 324/444, 324/691, 137/392, 137/5, 422/82.02
• US Class Current: 702/65
• CPC Class Codes: A47L 15/0049 Detection or prevention of malfunction, including accident prevention arrangements to prevent clogging of filters A47L15/4208; safety arrangements for preventing water damage A47L15/421
• CPC Class Codes: A47L 15/0055 Metering or indication of used products, e.g. type or quantity of detergent, rinse aid or salt; for measuring or controlling the product concentration
• CPC Class Codes: A47L 15/4297 Arrangements for detecting or measuring the condition of the washing water, e.g. turbidity
• CPC Class Codes: A47L 2401/30 Variation of electrical, magnetical or optical quantities
• CPC Class Codes: A47L 2501/26 Indication or alarm to the controlling device or to the user
• CPC Class Codes: G01N 27/045 Circuits measuring resistance per se G01R27/00, e.g. G01R27/22
• CPC Class Codes: G01N 27/06 of a liquid involving electrolysis G01N27/26
• CPC Class Codes: Y10T 137/6977 Escutcheon type support

Abstract

A conductivity measurement system provides one or more DC pulses to first and second electrodes submerged in an aqueous solution such as, for instance, the wash water of an industrial dishwasher. The voltage at the first electrode is measured at a sequence of at least three predetermined times after initiation of one of the DC pulse. A non-linear curve fitting function is applied to the sequence of at least three voltage measurements to calculate the voltage at the first electrode at the beginning of the DC pulse(s), commonly denoted as being at time t=0. The resulting calculated voltage at time t=0 is then used to calculate the conductivity of the solution, and/or to control operation of the a chemical dispenser, and/or to perform another predetermined system analysis or system control function. In addition, the difference between two of the measured voltages, such as the first and second measured voltages, is compared to a predetermined threshold value to determine whether the electrodes are so contaminated that polarization compensation is no longer feasible, thereby signaling that the electrodes should be cleaned or replaced.

Claims

1. A method of measuring representations of electrical conductivity of an aqueous solution which compensates for polarization, the method comprising:

generating a DC pulse to induce a current between first and second electrodes positioned within the solution;

sampling a voltage at the first electrode at a sequence of at least three predetermined time intervals after the generation of the DC pulse and generating a corresponding sequence of at least three voltage values in response thereto;

calculating, as a function of the at least three voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of the DC pulse; and

generating an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

2. The method of claim 1, wherein generating the output signal includes:

determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current flowing in the solution;

generating the output signal as a function of the calculated value and the current value.

3. The method of claim 1, wherein the solution contains a detergent having a concentration, the method further comprising:

mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

4. The method of claim 1, further comprising:

subtracting a first one of the at least three voltage values from a second one of the at least three voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

5. The method of claim 1, further comprising:

subtracting one of the at least three voltage values from another one of the at least three voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

6. The method of claim 1, wherein the calculated value is calculated using a linear approximation of a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

7. The method of claim 1, wherein the calculated value is calculated using a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

8. A method of measuring representations of the electrical conductivity of an aqueous solution which compensates for polarization, the method comprising:

generating a plurality of DC pulses to induce a current between first and second electrodes positioned within the solution;

sampling a voltage at the first electrode at a first predetermined time interval after the generation of one of the plurality of DC pulses and generating a first voltage value in response thereto;

sampling the voltage at the first electrode at a second predetermined time interval after the generation of another one of the plurality of DC pulses and generating a second voltage value in response thereto, wherein the one and the another one of the DC pulses are not the same DC pulse;

sampling a voltage at the first electrode at a third predetermined time interval after the generation of one of the plurality of DC pulses and generating a third voltage value in response thereto;

calculating, as a function of at least the first, second and third voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of one of the DC pulses; and

generating an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

9. The method of claim 8, wherein generating the conductivity signal includes:

determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current flowing in the solution;

generating the conductivity signal as a function of the calculated value and the current value.

10. The method of claim 8, wherein the solution contains a detergent having a concentration, the method further comprising:

mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

11. The method of claim 8, further comprising:

subtracting the first voltage value from the second voltage value to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

12. The method of claim 8, further comprising:

subtracting one of the at least three voltage values from another one of the at least three voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

13. The method of claim 8, wherein the at least first, second and third voltage values comprise a sequence of voltage values, and the calculated value is calculated using a linear approximation of a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of values.

14. The method of claim 8, wherein the at least first, second and third voltage values comprise a sequence of voltage values, the calculated value is calculated using a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of values.

15. Apparatus for measuring electrical conductivity of an aqueous solution, comprising:

a probe having first and second electrodes, for submersion in a tank containing the solution;

a circuit for generating a DC pulse to induce a current between the first and second electrodes within the solution; and

a controller programmed to;

sample voltage at the first electrode at a sequence of at least three predetermined time intervals after the generation of the DC pulse, and generate a corresponding sequence of at least three voltage values in response to the sampling of the voltage at the first electrode;

calculate, as a function of the at least three voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of the DC pulse; and

generate an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

16. The apparatus of claim 15, wherein the controller includes software executed by the controller for determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current in the solution, and for generating the output signal as a function of the calculated value and the current value.

17. The apparatus of claim 15, wherein the solution contains a detergent having a concentration, and the controller includes software executed by the controller for mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

18. The apparatus of claim 15, wherein the controller includes software executed by the controller for:

subtracting a first one of the at least three voltage values from a second one of the at least three voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

19. The apparatus of claim 15, wherein the controller includes software executed by the controller for:

subtracting one of the at least three voltage values from another one of the at least three voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

20. The apparatus of claim 15, wherein the calculated value is calculated using a linear approximation of a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

21. The apparatus of claim 15, wherein the calculated value is calculated using a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

22. Apparatus for measuring electrical conductivity of an aqueous solution, comprising:

a probe having first and second electrodes, for submersion in a tank containing the solution;

a circuit for generating first and second DC pulses to induce a current between the first and second electrodes within the solution;

a controller programmed to;

sample a voltage at the first electrode at a first predetermined time interval after the generation of one of the plurality of DC pulses and generate a first voltage value in response thereto;

sample the voltage at the first electrode at a second predetermined time interval after the generation of another one of the plurality of DC pulses and generate a second voltage value in response thereto, wherein the one and the another one of the DC pulses are not the same DC pulse;

sample a voltage at the first electrode at a third predetermined time interval after the generation of one of the plurality of DC pulses and generate a third voltage value in response thereto;

calculate, as a function of at least the first, second and third voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of one of the DC pulses; and

generate an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

23. The apparatus of claim 22, wherein the controller includes software executed by the controller for determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current in the solution, and for generating the output signal as a function of the calculated value and the current value.

24. The apparatus of claim 22, wherein the solution contains a detergent having a concentration, and the controller includes software executed by the controller for mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

25. The apparatus of claim 22, wherein the controller includes software executed by the controller for:

subtracting the first voltage value from the second voltage value to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

26. The apparatus of claim 22, wherein the controller includes software executed by the controller for:

subtracting one of the at least three voltage values from another one of the at least three voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

27. The apparatus of claim 22, wherein the at least first, second and third voltage values comprise a sequence of voltage values, and the calculated value is calculated using a linear approximation of a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

28. The apparatus of claim 22, wherein the at least first, second and third voltage values comprise a sequence of voltage values, and the calculated value is calculated using a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

29. Apparatus for measuring electrical conductivity of an aqueous solution, comprising:

a probe having first and second electrodes, for submersion in a tank containing the solution;

a circuit for generating one or more DC pulses to induce a current between the first and second electrodes within the solution;

means for sampling voltage at the first electrode at first, second and third predetermined time intervals after the generation of respective DC pulses of the one or more DC pulses;

means for generating first, second and third voltage values in response to the sampling of the voltage at the first electrode at the first, second and third predetermined time intervals, respectively, calculating, as a function of at least the first, second and third voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of any one of the one or more DC pulses; and

generating an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

30. The apparatus of claim 29, wherein the generating means includes means for determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current in the solution, and for generating the output signal as a function of the calculated value and the current value.

31. The apparatus of claim 29, wherein the solution contains a detergent having a concentration, and the generating means includes means for mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

32. The apparatus of claim 29, wherein the means for generating includes means for:

subtracting the first voltage value from the second voltage value to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

33. The apparatus of claim 29, wherein the means for generating includes means for:

subtracting one of the first, second and third voltage values from another one of the first, second and third voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

34. The apparatus of claim 29, wherein the at least first, second and third voltage values comprise a sequence of voltage values, and the calculated value is calculated using a linear approximation of a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

35. The apparatus of claim 29, wherein the at least first, second and third voltage values comprise a sequence of voltage values, and the calculated value is calculated using a nonlinear curve fitting function so as to compensate for nonlinearity, if any, in the sequence of at least three voltage values.

36. A method of measuring representations of electrical conductivity of an aqueous solution which compensates for polarization, the method comprising:

generating a DC pulse to induce a current between first and second electrodes positioned within the solution;

sampling a voltage at the first electrode at a sequence of at least two predetermined time intervals after the generation of the DC pulse and generating a corresponding sequence of at least two voltage values in response thereto;

calculating, as a function of the at least two voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of the DC pulse; and

generating an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

37. The method of claim 36, wherein generating the output signal includes:

determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current flowing in the solution;

generating the output signal as a function of the calculated value and the current value.

38. The method of claim 36, wherein the solution contains a detergent having a concentration, the method further comprising:

mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

39. The method of claim 36, further comprising:

subtracting a first one of the at least two voltage values from a second one of the at least two voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

40. A method of measuring representations of the electrical conductivity of an aqueous solution which compensates for polarization, the method comprising:

generating a plurality of DC pulses to induce a current between first and second electrodes positioned within the solution;

sampling a voltage at the first electrode at a first predetermined time interval after the generation of one of the plurality of DC pulses and generating a first voltage value in response thereto;

sampling the voltage at the first electrode at a second predetermined time interval after the generation of another one of the plurality of DC pulses and generating a second voltage value in response thereto, wherein the one and the another one of the DC pulses are not the same DC pulse;

calculating, as a function of at least the first and second voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of one of the DC pulses; and

generating an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

41. The method of claim 40, wherein generating the conductivity signal includes:

determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current flowing in the solution;

generating the conductivity signal as a function of the calculated value and the current value.

42. The method of claim 40, wherein the solution contains a detergent having a concentration, the method further comprising:

mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

43. The method of claim 40, further comprising:

subtracting the first voltage value from the second voltage value to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

44. Apparatus for measuring electrical conductivity of an aqueous solution, comprising:

a probe having first and second electrodes, for submersion in a tank containing the solution;

a circuit for generating a DC pulse to induce a current between the first and second electrodes within the solution; and

a controller programmed to;

sample voltage at the first electrode at a sequence of at least two predetermined time intervals after the generation of the DC pulse, and generate a corresponding sequence of at least two voltage values in response to the sampling of the voltage at the first electrode;

calculate, as a function of the at least two voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of the DC pulse; and

generate an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

45. The apparatus of claim 44, wherein the controller includes software executed by the controller for determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current in the solution, and for generating the output signal as a function of the calculated value and the current value.

46. The apparatus of claim 44, wherein the solution contains a detergent having a concentration, and the controller includes software executed by the controller for mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

47. The apparatus of claim 44, wherein the controller includes software executed by the controller for:

subtracting a first one of the at least two voltage values from a second one of the at least two voltage values to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.

48. Apparatus for measuring electrical conductivity of an aqueous solution, comprising:

a probe having first and second electrodes, for submersion in a tank containing the solution;

a circuit for generating first and second DC pulses to induce a current between the first and second electrodes within the solution;

a controller programmed to;

sample a voltage at the first electrode at a first predetermined time interval after the generation of one of the plurality of DC pulses and generate a first voltage value in response thereto;

sample the voltage at the first electrode at a second predetermined time interval after the generation of another one of the plurality of DC pulses and generate a second voltage value in response thereto, wherein the one and the another one of the DC pulses are not the same DC pulse;

calculate, as a function of at least the first and second voltage values, a value corresponding to the voltage at the first electrode at a time contemporaneous with the generation of one of the DC pulses; and

generate an output signal as a function of the calculated value, the output signal corresponding to the conductivity of the solution.

49. The apparatus of claim 48, wherein the controller includes software executed by the controller for determining a current flowing between the first and second electrodes and generating a current value in response thereto, the current value representing the current in the solution, and for generating the output signal as a function of the calculated value and the current value.

50. The apparatus of claim 48, wherein the solution contains a detergent having a concentration, and the controller includes software executed by the controller for mapping, using a look-up table, the output signal to a concentration signal representing the concentration of the detergent in the solution.

51. The apparatus of claim 48, wherein the controller includes software executed by the controller for:

subtracting the first voltage value from the second voltage value to generate a difference voltage;

comparing the difference voltage to a predetermined threshold voltage; and

generating an alarm signal if the difference voltage exceeds the predetermined threshold voltage, the alarm signal indicating that the electrodes are contaminated.